This image, from the Houston Clean Air Network Ozone Viewer, shows readings taken on Jan. 21, 2013, at 3:15 p.m., on a particularly bad air day in the region. At the Houston Clean Air Network's site, you can watch the plume grow and spread over the city over the course of several hours.

Jason Harris, with the Texas Commission for Environmental Quality, uses an infrared camera to find leaks at a chemical facility near the Houston Ship Channel. The specialty cameras cost around $100,000.

The Houston area produces about a quarter of the nation's gasoline, and about a third of the plastics that are in our cars, cupboards and just about everywhere else. So it is no surprise that this heavily industrial area has a problem with air pollution. But in the past decade, Houston's air has improved dramatically.

How that happened is a tale of good science, new technology and a Texas law that prompted companies along the Houston Ship Channel to disclose their emissions.

The channel is a muddy brown body of water that is surrounded by refineries, tank farms and about 200 petrochemical companies. It meanders inland from Galveston Bay toward downtown.

Dana Blume is standing on the deck of a fireboat plying the channel. She's been monitoring the air and water for the Port of Houston Authority for the past 14 years.

Summer here can bring misery. "It's hot; it's harder to breathe," she says. "I'm fortunate. I don't have respiratory issues. But I do worry about my child and other children who play on days that it's a high ozone day."

In recent years, those high ozone days come less often, and they're less intense when they strike.

"I can look out of my office window now and almost every single day see downtown. And that wasn't the case 10 years ago," Blume says.

To get the surprising back story about how Houston's air got cleaner, it's worth a visit to Harvey Jeffries, at the University of North Carolina's school of public health in Chapel Hill. As this retired professor tells the story, air pollution regulators were on the verge of making a multibillion-dollar mistake. They were going all-in against one of the pollutants that create smog, while downplaying the role of other emissions from the petrochemical plants.

Ozone (often called smog) forms when nitrogen oxides react in sunlight with chemicals called volatile organic compounds. Regulators were focusing their efforts overwhelmingly on nitrogen oxides, cranking down on them so hard that compliance would cost $4 billion a year. Jeffries says that was a big mistake.

"If you spent the $4 billion, if you did all the cleanup, they were controlling the wrong thing and ... they wouldn't do anything to prevent the true cause of the highest ozone," Jeffries says. He made that argument to the state and local officials.

Jeffries said the most bang for the buck would come from cutting back on volatile organic compounds like ethylene, which is used to make polyethylene plastic. Chemicals like these are produced in abundance along the ship channel.

"You're talking about billions of pounds of fluids and liquids a day, being produced in Houston. And if you only lose .001 percent of that, it's a massive amount of material, and that was being ignored, totally, completely," he says.

Jeffries pointed to a massive scientific study the state of Texas had funded in the year 2000. Results from that showed that volatile chemicals were a big culprit. Happily for industry, they were also a cheaper problem to fix.

It turns out that routine day-to-day emissions were not the biggest problem. On occasion, plants put out large bursts of chemicals. That could be when they were starting up or shutting down, or simply trying to avoid a disaster when a process went awry. Ethylene gas is commonly vented to the air.

"Ethylene is more explosive than hydrogen, and they're making billions of pounds of ethylene," Jeffries says. "And that's not something you want to fool around with. If there's likely to be a big back-pressure or something like this, you want a safety valve to go off."

But when a valve goes off, tens of thousands of pounds of these chemicals can vent into the air in a matter of minutes.

If the sun is beating down, and the wind is blowing in the right direction, a narrow plume of smog can form. Because smog forms over the course of a few hours, often these plumes appear in the suburbs, miles from the ship channel. Usually, a bad-air day in Houston is caused by one of these narrow plumes. It's often not a citywide miasma, as you find in Los Angeles or Dallas.

Scientists linked those plumes of smog to chemical "burps" thanks to a Texas law that required industry to report unexpected events in a public database.

"And as soon as all of this became visible, voila, it got cleaned up," Jeffries says.

Just a few years after Houston had won the title of the worst air in the country, residents finally tasted success. Beginning in 2005, when new standards went into effect, peak ozone concentrations started dropping sharply. And in 2009, Houston — for the first time in 35 years — met the federal air quality smog standard, Jeffries says.

A new technology helped tremendously. Regulators and companies bought cameras that "see" in infrared light. Invisible chemicals like ethylene show up as gray clouds in this camera.

"We did some flyovers of the ship channel," says Jason Harris from the Texas Commission for Environmental Quality. "We attached [an infrared] camera to a helicopter and flew over the industrial areas and saw some pretty eye-opening things."

Barges carting chemicals up and down the channel were leaking chemicals that contribute to smog in the air. And some types of storage tanks were leaking as well.

Steve Smith from the chemical giant LiondellBassell says his company didn't want to lose its products to the air, so it bought nine of the infrared cameras, at about $100,000 apiece, to find its own leaks.

"We are able to fix things sooner and we're able to fix the right things," Smith says, since the cameras easily pinpoint leaks. "And therefore we can do the right thing sooner and obviously have lower emissions and a cleaner environment."

This also saves the company money, by reducing its pollution taxes and potential fines.

Larry Soward was one of the commissioners on the Texas environmental board during those critical years when Houston's air improved. He says getting industry to this point wasn't quite as painless as you hear tell these days.

"Early on they came kicking and screaming because it meant either major investment for technology or it meant major operational changes," he says.

Gradually, many companies came to realize that tightening up their leaks and reducing accidental releases gave them a competitive advantage.

But there is still work to be done. Houston, the nation's fourth largest city, still doesn't meet the federal smog standard most of the time. And getting there will involve more than industry.

In February, we met up with Matthew Tejada, who was head of the region's only nonprofit organization dedicated to the issue of clean air: Air Alliance Houston. (Tejada has since taken a job as director of the Office of Environmental Justice at the U.S. Environmental Protection Agency.)

Tejada drove us through the sprawling city. He said if you add up all the gas stations, print shops and dry cleaners, they actually put more smog-producing volatile organic compounds into the air than the refineries do. "The unique thing you have to remember, though, especially when you're talking about ozone, is a print shop can't release 100,000 pounds of VOC in five minutes," Tejada says. "One of these facilities on the ship channel can."

So the little guys and the big guys will both get a hard look as regulators search for ways to ratchet back smog.

So will transportation. Cars are much cleaner than they used to be, but they're still a major source of smog for Houston. And people drive everywhere — public transportation here is not much of an option.

Tejada says even if Houston can do more to reduce emissions from industries, businesses, cars and trucks, the city still won't be able to meet the ozone standard. The federal limit is currently 75 parts per billion — and there are days when air blowing into Houston is already loaded up with 50 or 60 parts per billion of ozone.

"We're going to have to go out and find out where that ozone's coming from and make them clean up," Tejada says.

What's more, the city's population is expected to double by 2030, which means there will be many more sources of pollution. And, with the recent boom in natural gas in Texas, the petrochemical industry is poised to grow rapidly in the next decade.

"What's the bigger picture for the Houston region if in the next 10 years we build five new gas processing facilities?" Tejada asks. "What's that going to do for our air quality picture? I think we're very slow to look at the holistic implications of what that will mean for the Houston region."

But in a city that is dependent on the petrochemical industry, those questions get asked only as an afterthought.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

RENEE MONTAGNE, HOST:

NPR aired a series last year called Poisoned Places about regions living with industrial pollution. We're reviving that series this week, but the news isn't all grim. This morning we take a look at a city that has cleaned up its air: Houston.

DAVID GREENE, HOST:

That metropolitan area is home to hundreds of petrochemical plants. They produce about a quarter of the nation's gasoline and about a third of the plastics that are in our cars, cupboards and just about everywhere else. In the last decade, Houston's air has improved dramatically.

MONTAGNE: How that happened is a tale of new technology and a Texas law that prompted companies to disclose what they were emitting. NPR's Richard Harris has the story.

RICHARD HARRIS, BYLINE: If you want to get to the heart of Houston's petrochemical industry, take a trip out onto the Houston ship channel. It's a muddy brown body of water that's surrounded by refineries, tank farms and petrochemical companies as it winds inland from Galveston Bay toward downtown. Dana Blume is standing on the deck of a fireboat plying the channel. She's been monitoring the air and water for the Port of Houston Authority for the past 14 years. And she says you sure notice those smoggy summer days.

DANA BLUME: It's hot. It's harder to breathe. I mean I'm fortunate. I don't have respiratory issues. But I do worry about my child and other children who play on days that it's a high ozone day.

HARRIS: In recent years, those high ozone days have come less often, and they're less intense when they do strike.

BLUME: I can look out of my office window now and almost every single day see downtown. And that wasn't the case 10 years ago.

HARRIS: To get the surprising back story about how Houston's air got cleaner, it's worth a visit to Harvey Jeffries at the University of North Carolina's School of Public Health in Chapel Hill. As this retired professor tells the story, air pollution regulators were on the verge of making a multibillion dollar mistake. This involves a little chemistry. Ozone is created in the air when one kind of pollution - nitrogen oxide - reacts in sunlight with chemicals called volatile organic compounds. Regulators were focusing their efforts overwhelmingly on nitrogen oxides, cranking down on them so hard, compliance would cost $4 billion a year. Jeffries says big mistake.

HARVEY JEFFRIES: If you spent the $4 billion, if you did all the cleanup, they were controlling the wrong thing and they wouldn't do anything to actually prevent the true cause of the highest ozone.

HARRIS: Jeffries says, sure, you need to control nitrogen oxides, but the most bang for the buck would come from cutting back on volatile organic compounds like ethylene, which is used to make polyethylene plastic. Chemicals like these are produced in abundance along the ship channel.

JEFFRIES: You're talking about billions of pounds of fluids and liquids a day being produced in Houston. And if you only lose .001 percent of that, it's a massive amount of material, and that was being ignored, totally, completely.

HARRIS: Jeffries pointed to a massive scientific study the state of Texas had funded in the year 2000. Results from that showed that volatile chemicals were a big culprit, and happily for industry cheaper to fix. And it wasn't just the day-to-day emissions but big unexpected releases. For instance, sometimes plants released potent chemicals like ethylene in order to prevent a catastrophe.

JEFFRIES: Ethylene is more explosive than hydrogen, and they're making billions of pounds of ethylene. And so it's not something that you want to sort of fool around with. And if there's likely to be a big back-pressure or something like this, you want a safety valve to go off.

HARRIS: And when a valve goes off, tens of thousands of pounds of these chemicals can vent into the air all at once. If the sun is beating down and the wind is blowing in the right direction, a narrow plume of smog can form. Because smog forms over the course of a few hours, often these plumes appear in the suburbs, miles from the ship channel. Typically now, a bad air day in Houston is caused by one of these narrow plumes, not a citywide miasma, as you find in Los Angeles or Dallas. Scientists link those plumes of smog to these chemical burps thanks to a Texas law that required industry to report unexpected events in a public database.

JEFFRIES: And as soon as all of this became visible, voila, it got cleaned up.

HARRIS: Just a few years after Houston had won the title of the worst air in the country, residents finally tasted success.

JEFFRIES: Beginning in 2005, '6, '7, the peak ozone concentration dropped in a straight line, until in 2009 Houston achieved - for the first time in 35 years - the ambient ozone standard that was in effect at that time.

(SOUNDBITE OF CONSTRUCTION)

HARRIS: It's not only that scientists had finally identified he problem; they also had a new technology to help them address it. That's a camera that can see what the human eye cannot. It looks at infrared light. And when a chemical like ethylene is in the air, it appears in the infrared camera like a dark cloud. Jason Harris from the Texas Commission on Environmental Quality was on the side of the road just north of the Houston Ship Channel one winter morning, looking out at tank farms for signs of leaks.

JASON HARRIS: We look at any and all sources we can see from roadways or other public areas. You know, we're looking for those unrecognized or unauthorized emission sources.

HARRIS: And in a typical day, do you see a leak or do you not see a leak?

HARRIS: I'd say more often than not we don't find anything, which is good news.

HARRIS: But in the early days of this technology, it was quite a different story.

HARRIS: We did some flyovers of the ship channel. We attached a similar camera to a helicopter and flew over the industrial areas and saw some pretty eye-opening things.

HARRIS: Barges carting chemicals up and down the channel turned out to be leaking this stuff into the air. And some types of storage tanks turned out to leak as well. Steve Smith from the chemical giant LiondellBassell says his company didn't want to lose its products into the air, so they bought nine of the infrared cameras, at about $100,000 apiece, to find their own leaks.

STEVE SMITH: And we are able to fix things sooner and we are able to fix the right things as opposed to thinking that it might be one problem when in fact the camera shows us something different. And therefore we can do the right thing sooner and obviously have lower emissions and a cleaner environment.

HARRIS: And, of course, save the company money by reducing its pollution taxes and avoiding potential fines. Larry Soward was one of the commissioners on the Texas environmental board during those critical years when Houston's air improved. He says getting industry to this point wasn't quite as painless as you hear tell these days.

LARRY SOWARD: Well, early on they came kicking and screaming because it meant either major investments for technology or it meant major operational changes.

HARRIS: But change they did, and gradually many companies came to realize that tightening up their leaks and reducing their accidental releases gave them a competitive advantage.

SOWARD: At least you're leading industry, you're, you know, some of your ExxonMobils, your LiondellBassells, those type of industries really began to see that it was in their economic benefit to not only comply but to get ahead of the curve.

HARRIS: The question now for these industries - in fact for all of Houston - is what next? Despite all the improvement, the air quality still falls short of increasingly stringent federal health standards. Richard Harris, NPR News.

(SOUNDBITE OF MUSIC)

MONTAGNE: Tomorrow, we'll hear how getting that next big improvement could be tough. Poisoned Places is a collaboration with the Center for Public Integrity. Transcript provided by NPR, Copyright NPR.